Hey Stephenie Meyer fans, have we got a treat for you. MTV News got a behind-the-scenes look at Andrew Niccol's big-screen adaptation of Meyer's "The Host."The sci-fi romance is Meyer's first adult novel, and we were lucky enough to get an exclusive sneak peek when we visited the set last month.

"The Host" is the story of Melanie Stryder (played by Saoirse Ronan), one of the last humans to have avoided capture by an alien race called Souls. The Souls operate more like parasites in that they invade human bodies and erase their personalities. The film follows the unlikely partnership of Melanie and her parasite as they seek out the last of Melanie's human relatives and her love Jared (Max Irons).

For Ronan, whom we witnessed running down corridors and jumping off tall precipices, her dual roles are a lot more physical than she expected, but she has relished the opportunity to flex those new action-type muscles.

"I didn't expect it to be so physical. I've been in a harness quite a bit, I've done stunts, I jumped off a balcony it was 30 feet in the air," Ronan revealed with pride. "That was pretty cool."

Speaking to the film's romance, Irons admitted that he enjoyed the struggle Jared has in wanting to be close to Melanie, but knowing in the back of his mind that he can't. We watched Ronan and Irons film one of their more emotionally charged scenes that involved Jared trying not to kiss Melanie.

"Jared's struggle is when Melanie returns, she was the love of his life and he lost her, but then she walks back into his life," Irons explained. "He wants to hold her, but the rational part of his mind is saying she needs to be killed."

From the looks of things on set, this big-screen adaptation has major potential to strike a chord among Meyer's dedicated fanbase. The author told us that she's enjoyed her involvement in the production and that being on the cave sets was particularly magical for her.

"It was so awesome. The cave set was enormous, it was vast, they're just so cool, so much fun to walk on," Meyer enthused. "It was kind of like someone built something out of your imagination just for you."

The also stars Jake Abel, William Hurt and Diane Kruger, and is slated for a March 2013 release.